CHAP. 111. ORIGIN OF WOOD. 267 



ino- sap. The first of these opinions appears to be that of 

 Turpin, as far as can be collected from a long memoir upon 

 the grafting of plants and animals. The second is the opinion 

 commonly entertained in France, and adopted by De Candolle 

 in his latest published work. 



The objections to the views of Turpin need hardly be 

 stated. Those which especially bear upon the view taken by 

 De Candolle are, that his theory is not applicable to all parts 

 of the vegetable kingdom, but to exogenous plants only ; that 

 it is inconceivable how the highly organised parallel tubes of 

 the wood, which can be traced anatomically from the leaves, 

 and which are formed with great rapidity, can be a lateral 

 deposit from the liber and alburnum ; that they are manifestly 

 formed long before it can be supposed that leaves have 

 commenced their office of elaborating the descending sap; 

 and, finally, tbat endogens and cryptogamic plants, in which 

 there is no secretion of cambium, nevertheless have wood. 



Such is the state of this subject at the time I am writing. 

 To vise the words of De Candolle, " The whole question may 

 be reduced to this — Either there descend from the top of a 

 tree the rudiments of fibres, which are nourished and deve- 

 loped by the juices springing laterally from the body of wood 

 and bark ; or new layers are developed by pre-existing layei-s, 

 which are nourished by the descending juices formed in the 

 leaves." 



As this is one of the most curious points remaining to be 

 settled among botanists, and as it is still as much open to 

 discussion as ever, I have dwelt upon it at an unusual lengdi, 

 in the hope that some one may have leisure to prosecute the 

 inquiry. Perhaps there is no mode of proceeding to eluci- 

 date it which would be more likely to lead to positive results, 

 than a very careful anatomical examination of the progres- 

 sive development of the mangel wurzel root, beginning with 

 its dormant embryo, and concluding with the perfectly formed 

 plant. 



